An important function of emergency lighting devices in a closed building is to illuminate emergency exits in case of an evacuation of the building is needed. Such scenarios might be a fire alarm or a mains voltage breakdown or the like. An emergency light device therefore comprises a self-sustaining voltage supply, which is used to supply energy to an emergency light source in case of the mains voltage loss. This voltage supply comprises an energy storage unit—e.g. a rechargeable battery—as its basic element, which is charged by means of a mains voltage supply unit during normal operating conditions and which is used as an energy supply in case of a mains voltage failure to supply the lighting means.
Such emergency lighting devices are well known from prior art document EP 2 249 459 A1. Therein a voltage supply is described which comprises an energy storage unit for supplying an emergency lighting means, a driving unit for driving the emergency lighting means, a charging unit for recharging the energy storage unit in normal-mode conditions and a control unit for controlling the emergency lighting device. In the known emergency lighting devices a boost converter is used to boost the voltage from the energy storage unit to a supply voltage, which is required for the controlling unit and the driving unit.
The controlling unit and the driving unit of the voltage supply are mainly built by integrated circuit devices.
To ensure a maximum lifespan of the energy storage unit, the control unit is configured to obtain operation commands to extinguish the emergency lighting means if the mains voltage supply still fails after a certain timespan. Such an operation command limits the number of continual charge/discharge cycles and reduces the stress on the emergency storage unit. According to standardized requirements, the maximum current drain of the energy storage unit shall not exceed a specific predetermined amount of current, if the emergency lighting device is operated based on such an operation command.
Additionally, there exist standardized operation commands to re-light the emergency lighting device. Some integrated circuit devices in the emergency lighting device therefore need to be operated with a start-up voltage above a certain voltage value. Other integrated circuit devices might not need such a high start-up voltage.
However, such high start-up voltages of the integrated circuit devices prohibit the predetermined maximum drain current value from not being exceeded and therefore nowadays voltage supplies for emergency lighting devices fail the standardized requirements.
As long as the voltage of the battery of the emergency device is higher than a first threshold, the energy supply unit is in a condition that a controlling unit is fully operative and the emergency lights are operated. As soon as the voltage falls below a given threshold value or a corresponding command is received from the first bus, the system will assume a so-called REST-mode in order to extinguish the emergency lights. However, the controlling unit is still operative. During this REST-mode, the controlling unit can still receive or send out commands. A typical power consumption in the REST-mode may be in the order of several Milliampere for a battery having a capacity of two ampere hours.
It is therefore an objective of the invention to provide a voltage supply unit for a lighting means which fulfills the standardized requirements, for instance using a first bus, for instance a digital addressable lighting interface, short DALI
Another objective of the invention is to ensure that the standardized maximum current drain of the energy storage unit is not exceeded, for instance as defined in standard document EN 60598-2-22
Another objective of the invention is to drastically reduce the power consumption of an emergency power supply unit when a certain threshold voltage of a self-sustaining energy storage unit is undershot to relax the energy storage unit.
The invention should cover the requirements according to EN 61347-2-7 that are referred to lamp control gears and comprise particular requirements for energy storage unit supplied electronic control gear for self-contained emergency lighting devices.
The invention should cover the requirements according to EN 62034 that are referred to automatic test systems for energy storage unit powered emergency escape lighting devices.
The invention should cover the requirements according to EN62386-202 that are referred to the digital addressable lighting interface, DALI, particular requirements for the control gear and self-contained emergency lighting devices.
These objectives are solved by the technical features described herein.